Have you heard of the Mano Secreto? It is the secret hand technique used and first made popular by percussion legends Changuito and also Giovanni Hildago. Prior to these great conga players there was another player named tat Guines in Havana Cuba who was developing this technique. Why is it secret? Because until recently (well about 10 years or so ) no one else could do it. Now everyone is doing it but there are not a lot of great instructional videos about it unfortunately.